This invention relates to strip materials that have headed projections which will releasably engage so that two severed portions of the strip materials will provide a releasable fastener between different objects.
U.S. Pat. Application Ser. No. 869,132, now U.S. Pat. No. 4,290,174, describes such a strip material which comprises a flexible polymeric bonding layer; a multiplicity of flexible, resilient, generally U-shaped monofilaments of polymeric material, each including a central bight portion embedded in the bonding layer, two stem portions extending from the bight portion and projecting generally normal to a surface of the bonding layer; and enlarged, generally circular heads at the distal ends of the stem portions. Each of the heads has an outer cam surface adapted for engagement with the cam surfaces of heads along a different portion of the strip material to produce deflection of the stem portions and movement of the heads on the stem portions past each other to releasably engage the portions, and has a latching surface opposite the cam surface, which latching surface is generally planar, extends at generally a right angle radially from its supporting stem portion, and is adapted to engage similar latching surfaces on the heads of the other portion when the portions are engaged.
While fasteners made from two portions cut from the strip material described in U.S. Pat. Application Ser. No. 869,132 have provided many advantages over other known fasteners for many applications, problems have been encountered when those portions are engaged with their rows of headed projections aligned, and when forces are subsequently applied to the two fastener portions in a direction parallel to their backing layers and aligned with the rows. Under these conditions, the rows of headed projections on one portion can slide between the rows of headed projections on the other portion, and allow the portions to become partially or totally disengaged. U.S. Pat. Application Ser. No. 869,132 teaches reducing this problem by (1) varying the spacings of the stems along the rows extending longitudinally of the strip so that at least when the rows of two articles with such varied spacing are engaged at right angles to each other, greater separating and shear strengths will be developed, or (2) disposing the rows of U-shaped filaments so that their stems are not aligned normal to or parallel with the edges of the strip so that when a user engages two articles made from the strip with their edges aligned (as he would normally be expected to do), the rows on the articles will cross each other to develop the maximum strength in the fastener both in tension and shear, or (3) shifting successive rows of U-shaped filaments slightly in a direction transverse to the strip so that the stems of successive rows will not be aligned and thus will not permit shearing longitudinally to the strip.
While these techniques would help reduce the problem, they do not preclude slippage between the rows for all possible orientations of the rows. Additionally, the mechanism for accomplishing the second and particularly the third techniques mentioned complicate the device on which the strip material is produced moe than might otherwise be desired.